The International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) group is a new Leadership Group representing a merger of investigators from the Pediatric AIDS Clinical Trials Group (PACTG) and the Perinatal Scientific Working Group of the HIV Prevention Trials Network (HPTN/HIVNET). The group will be headed by the group chair, Brooks Jackson, MD, MBA (Johns Hopkins). Social & Scientific Systems, Inc. (SSS), will be the Coordinating and Operations Center (CORE). The Statistical Data Management Center (SDMC) for the IMPAACT group will be SDAC/FSTRF headed by Terence Fenton, Ed.D (Harvard). The Central Laboratory Network for the group will be headed by Susan Fiscus, PhD (U North Carolina).The mission of the IMPAACT group, which is worldwide in scope, will be to significantly decrease the mortality and morbidity associated with HIV disease in pregnant women, infants, children, and adolescents by: 1) Developing and evaluating safe and cost effective approaches for the interruption of mother-to infant Transmission; 2) Evaluating treatments for HIV-infected children, adolescents, and pregnant women, including treatment and prevention of co-infections and co-morbidities; 3) Evaluating vaccines for the prevention of HIV sexual transmission among adolescents. IMPAACT has an ambitious scientific agenda which proposes to carry forward 28 PACTG, four HPTN, and one ATN treatment and prevention trials (transition protocols) and develop 26 new protocols. In the first year, we estimate that IMPAACT will enroll and/or follow approximately 9,434 women, children, and adolescents in developing countries into 23 protocols (eight new and 15 transition protocols) and 1,479 subjects in the United States into 19 protocols (four new and 15 transition protocols). These protocols will be in four of the six RFA-designated high-priority areas (PMTCT, translational research/drug development, optimization of clinical management including co-morbidities, and vaccines). Due to the requirements of the RFA, HIV vaccine trials for prevention of breastfeeding transmission are described and budgeted in the PMTCT section, therapeutic vaccine trials in the translational research section, and HIV prophylactic vaccine trials for adolescents and preadolescents to prevent sexual transmission in the Vaccine section.